1. Field of the Invention
This invention relates to solder compositions; a method of soldering, to make electrical connections, a laminated transparency having bus bars, and more particularly, to a solder having a low melting temperature so that the heat of a manufacturing process can be used to melt the solder, e.g. using the heat of a windshield laminating process to laminate two glass sheets together and to melt the solder.
2. Discussion of the Technical Problem and Available Solutions
In the manufacture of laminated transparencies, e.g. automotive windshields, having an electrically conductive member between laminated glass sheets, e.g. heatable coatings and/or antennas to transmit or receive signals, leads extend outward from between the laminated glass sheets to provide external electrical access to the conductive member. U.S. Pat. No. 5,861,606 (“Pat. '606”) discusses a bus bar system having a plurality of spaced wires between and connected to a pair of spaced bus bars. Bus bars strips extend from the upper bus bar to the bottom portion of the windshield spaced from the electrically conductive wires and the bottom bus bar. End portions of the upper bus bar and upper end portions of bus bar strips are soldered together during autoclaving. One of the glass sheets of the windshield is provided with a recess to expose end portions of the lower bus bar and lower end portions of the bus bar strips. Leads are soldered to the lower bus bar and the bus bar strip prior to or after autoclaving.
A limitation of soldering leads in accordance to the method disclosed in Pat. '606 is the localized heating of the glass sheet during soldering. U.S. Pat. No. 6,253,988 (“Pat. '988”) discusses the problems associated with localized heating of glass during soldering. More particularly, Pat. '988 discloses that solder typically used for soldering leads to contacts of an electrical component has a melting point of about 193° C. (380° F.) and, if resistance soldered, requires about 750-800 waft seconds of energy to melt the solder. During soldering, heat flows on the glass sheet in regions near the solder joint, and heat of this magnitude may be sufficient to cause damage to the glass sheet, e.g. initiate stresses in the glass during soldering due to temperature differences, which can cause glass chipping.
One technique to eliminate the localized heating discussed in Pat. '988 is to use the bus bar system disclosed in U.S. patent application Ser. No. 10/201,863 filed on Jul. 24, 2002, in the names of Bartrug et al. for “Edge Sealing of a Laminated Transparency” (hereinafter also referred to as “U.S. Ser. No. 10/201,863”). In general, the bus bar system includes a “T” shaped metal foil bus bar having one leg of the “T” extending beyond the laminated sheets, and the other leg of the “T” in electrical contact with the conductive member. The solution to eliminate localized heating provided by Pat. '988 is to solder at lower temperatures. More particularly, Pat. '988 discloses a solder having a solidus temperature of 118.5° C. (245.3° F.) and a liquidus temperature of 121.5° C. (250.7° F.). The solder can be melted with energy levels in the range of 250 to 650 watt second. Using the solder of Pat. '988 with the solder process discussed above, e.g. in Pat. '606, to solder leads to bus bars and/or bus bar strips, can reduce the occurrence and/or magnitude of glass chipping due to localized heating. However, the soldering method of Pat. '988 still requires a separate soldering step to solder the leads to the bus bars. Further, the problem of localized heating still exists when using high temperature melting solders.
As can be appreciated, it would be advantageous to provide a method of soldering or bonding electrical members or components carried on a glass sheet that eliminates the separate soldering step and eliminates localized heating of glass during soldering thereby eliminating damage to the glass sheet, e.g. glass chipping, and to provide an additional solder composition that has a low melting temperature.